Epidemiological studies in naturally infected persons have shown that there is a significant relation between antibody levels to the current circulating virus and morbidity. Serological findings and morbidity data suggest: (1) that the serological survey is a more sensitive indicator for influenza outbreaks than is the clinical diagnosis and (2) that the 5-14 age group is first affected when an epidemic of influenza starts off. Consequently, school children may be the major source of influenza into family units and, therefore, among older segments of the population.
Exploring the relationships between influenza morbidity and natality, as well as influenza morbidity and mortality under 1 year of age, values of <0·001 (Student's t-test) were obtained. The linear regression analysis showed that both relationships were represented as straight lines.
From the results it seems logical to utilize the available vaccine for the protection of infants, school children and pregnant women. The vaccine-induced protection can offer significant, although not total, protection of the whole population and prevent obstetrical accidents.